A smoke detecting device generally comprises, for example, a base secured to a ceiling or the like, a body removably set to the bottom of the base, and an outer cover for covering the face (bottom) opposite to the base of the detecting body.
The detecting body comprises a circuit part comprising a printed circuit board on which electronic parts serving as a fire detecting circuit are mounted, a detecting part serving as a sensor for detecting smoke, and a body to which the circuit part and the detecting part are secured and which is removably set to the base. The detecting device may be based upon either an ionization or photoelectric detection.
In ionization detection, the detecting part has, for example, an inner electrode having a radiation source, an intermediate electrode set so as to face the inner electrode, and an outer electrode (outer chamber) formed so as to cover the opposite side to the inner electrode of the intermediate electrode, in which the gap between the inner electrode and the intermediate electrode is formed as an almost-closed inner ionization chamber and the gap between the intermediate electrode and the outer chamber is formed as an outer ionization chamber allowing smoke to enter from the outside.
An opening is formed on the intermediate electrode so that the radiation emitted from the radiation source provided for the inner electrode can be also irradiated to the outer ionization chamber. The ionization smoke detecting device uses a field effect transistor (hereafter referred to as FET) for detecting a potential change at the joint between the inner and outer ionization chambers and the intermediate electrode is connected to the FET. Because an ionization smoke detecting device has a relatively complicated structure having an inner ionization chamber and an outer ionization chamber as described above, the detecting device has problems that it takes a lot of time to assemble and set the detecting device and it is difficult to decrease the cost.
For example, in the case of the FET, the insulation between terminals may be deteriorated due to humidity or dust. Therefore, it is preferable to use the FET in a closed state. Moreover, it is necessary that an intermediate electrode connected to the FET is set so as to face an inner electrode under an insulated state. Therefore, it is troublesome to set the FET and intermediate electrode.
Photoelectric detection includes a detecting device for detecting an infrared (IR) light source and an IR photodiode receiver positioned at opposite ends of a detection chamber. They are located off axis from each other to prevent the IR light source emitted energy from flowing directly to the receiver. Light absorbing baffles and coatings within the chamber are used to attenuate all quiescent state IR reflections, to provide a controlled, minimum value of photodiode current in the non-smoke state. In the event of a fire, combustion particles entering the device's chamber disturb the quiescent state absorption characteristics, thereby producing IR scattering and causing IR energy to be detected by the photodiode. The photodiode responds by providing an output electrical current at a magnitude proportional to the detected IR, and when the current exceeds a selected threshold the device sounds the alarm. Existing types of carbon monoxide detecting devices can be broadly classified into one of four types according to the gas sensitive element employed: chemical, electrochemical, semiconducting or spectroscopic (infra-red). The electrochemical and spectroscopic devices, whilst offering rapid response times, high resolution and high accuracy, are expensive and not suitable for domestic use. Chemical sensors are inexpensive devices that are usually based on palladium or iodine salts which exhibit a color change upon exposure to CO. They are of two classes; tapes for continuous monitoring which can provide very fast and sensitive response (typically sub ppm concentrations are sensed) but these require very careful control over moisture content and tubes which are used for spot checks and are of generally lower sensitivity than tapes although they do not require such careful control of moisture. Both types rely on a color change and could not be made “automatic” by the application of an electronic device the degree of color change. These devices are not reusable. However, their response to low CO concentrations tends to be poor and therefore constant monitoring is required and can only be used once and fail to provide audible warning signals.
The most popular carbon monoxide detecting devices for domestic use utilize a gas sensitive semiconductor; the resistance of which changes upon exposure to a reducing gas. Of these the most popular material is SnO2 and platinum doped SnO2 other binary oxides include ZnO, TiO2 and a combination of CuO and ZnO to form a heterocontact. More recently the use of mixed metal oxide semiconductors for CO detection has been reported. These materials include the niobates CrNbO4, FeNbO4 and Ba6Fe1.5Nb8.5O30 and the perovskite La0.5Sr0.5C03.
Weather radio receivers for use with the National Oceanic and Atmospheric Administration Weather Radio (NWR) service are widely available and incorporate various features according to cost and manufacturer. The most basic receiver feature consists of providing an emergency alert notification in response to a NWR broadcast describing an event that threatens life or property.
The National Weather Service (NWS) uses an NWR-Specific Area Message Encoding (NWR-SAME) scheme. By placing encoded information at the beginning and end of each emergency broadcast, the NWR-SAME scheme permits greater control of transmitters, receivers, and other broadcasting equipment within a specific geographic region. The encoded information is transmitted on NWR radio channels using audio frequency shift keying (AFSK) and contains information describing the emergency and the NWR-SAME emergency alert broadcast. Aspects of this information may include, for example, the emergency type, the geographic area affected, the expected duration of time for which the information contained in the emergency alert broadcast is valid, the date and time of the broadcast, and the identity of the broadcast originator. A weather radio receiver capable of interpreting this information may be programmed to provide an emergency alert notification in response to receiving a NWR-SAME broadcast only if user-defined emergency alert preferences such as, for example, the emergency type and the geographic area affected, are satisfied.